Acrylic copolymer, acrylic pressure-sensitive adhesive composition, acrylic pressure-sensitive adhesive tape or sheet, and acrylic adhesive composition

ABSTRACT

Acrylic copolymers are provided which have polymeric portions having different polarities or glass transition temperatures, which permit easy selection of combinations of such polymeric portions having different polarities or glass transition temperatures, which increase a design freedom and which are applicable for diverse uses. 
     Acrylic copolymers including a polymeric backbone portion prepared via copolymerization of (a) an alkyl (meth)acrylate ester containing 1-14 carbon atoms in the alkyl, (b) an olefinic polymer or copolymer terminally modified by a free-radically polymerizable unsaturated double bond and (c) a polymer terminally modified by a free-radically polymerizable unsaturated double bond and having a number average molecular weight of 2,000-30,000 and a glass transition temperature of at least 30° C. and comprised chiefly of the alkyl (meth)acrylate ester, and a polymeric branch portion grafted to the polymeric backbone portion and having a lower polarity and different glass transition temperature than the polymeric backbone portion.

TECHNICAL FIELD

The present invention relates to an acrylic copolymer and an acrylicpressure-sensitive adhesive composition. More particularly, the presentinvention relates to an acrylic copolymer which contains polymericportions having distinguished polarities and thus provides an excellentdesign freedom for application to various uses, also to an acrylicpressure-sensitive adhesive composition using the acrylic copolymer,further to an acrylic pressure-sensitive adhesive tape or sheet, andfurther to an acrylic hot melt adhesive composition.

BACKGROUND ART

In recent years, there has been an increasing demand forhigh-performance or high-function polymeric compounds. This has led usto recognize the importance of high-molecular weight polymers, graft andblock copolymers containing different polymeric portions. For example,Japanese Patent Laying-Open No. Sho 62-235310 discloses a method formanufacturing a block copolymer by sequentially polymerizing two typesof monomer mixtures, with the use of a bifunctional peroxide catalystcontaining two types of peroxy bonds that decompose at differenttemperatures in a molecule, to thereby allow rubber-constitutingpolymeric portions to undergo copolymerization with resin-constitutingpolymeric portions.

However, monomers applicable for use in this method are limited tohighly polar unsaturated alkyl carboxylate esters and aromatic vinylcompounds. This has inevitably led to an increase in polarity of aresulting block copolymer as a whole.

Japanese Patent Laying-Open No. Sho 59-75975 discloses a method formanufacturing an acrylic graft copolymer by utilizing a macromonomerhaving a high glass transition temperature. However, this methodutilizes high-polarity monomers, as similar to the case of the aforesaidblock copolymer, to inevitably result in the increased polarity of aresulting graft copolymer as a whole.

Japanese Patent Laying-Open No. Sho 59-75975 also discloses an acrylicpressure-sensitive adhesive made by utilizing the above-described graftcopolymer. However, the highly polar character of the graft copolymerutilized not only limits the types of applicable tackifying resins butalso prevents the adhesive to build desired adhesive strength relativeto low-polarity adherends.

Notwithstanding the above, the acrylic pressure-sensitive adhesives havegained wider acceptance compared to rubber pressure-sensitive adhesivesfor their increased cohesion and superior resistance to weather andsolvent.

As one exemplary means of enhancing adhesion of the acrylicpressure-sensitive adhesive to an adherend having a low-polaritysurface, such as polyethylene or polypropylene, Japanese PatentLaying-Open No. Hei 3-281587 discloses a composition incorporating aresinate ester in an acrylic polymer.

However, the acrylic pressure-sensitive adhesive composition describedin the above-identified prior art still suffers from the highly polarcharacter of the acrylic polymer per se. This has limited the types ofapplicable tackifying resins and led to the failure to reduce thedifference in polarity between the adhesive composition and alow-polarity adherend to a level sufficient for them to build asatisfactory adhesive strength.

Apart from the above, synthetic resin films or sheets have achieved wideuse for purposes of protecting various parts. That is, such protectivefilms or sheets are widely used for protecting a metal sheet made ofstainless steel or aluminum, a precoat steel, a decorative sheet, aplastic sheet or an aluminum sash, while it is machined, cured ortransported.

For example, in Japanese Patent Laying-Open No. Sho 61-103975, anadhesive film for surface protection is disclosed which is made byapplying onto a polyolefin substrate a pressure-sensitive adhesive layerformed from a composition containing, by weight, 100 parts of A-B-A (Arepresents a styrene polymer block and B represents an ethylene-butylenecopolymer block) and 0-80 parts of a tackifying resin. While providingsatisfactory anchoring effect, the adhesive film for surface protectiondescribed in this prior art has been still insufficient in terms ofweather resistance.

This has led to the use of a protective film prepared by solutioncoating an acrylic pressure-sensitive adhesive on a vinyl chloride resinor polyolefin substrate for uses requiring outdoor protection,particularly resistance to weather and light. However, since this typeof protective film must be removed from a part on which the film hasbeen applied for protection before the part is put into use, it isconstructed to be readily releasable from the part. For example, asilicone oil or other release agent is loaded in the acrylicpressure-sensitive adhesive to insure enhanced releasability. However, asurface of the protected part is stained by the release agent, which hasbeen a problem.

Also, solvent-free hot-melt adhesives have gained an increasing noticeas a result of the recent severe criticism on environmental pollutioncaused by solvent-incorporated adhesives, and also from a viewpoint ofsaving energy and resources. Those comprised principally of anethylene-vinyl acetate copolymer establish a current mainstream ofhot-melt adhesives for their superior hot-melting and flow propertiesand compatibility with other resins. Notwithstanding these notedadvantages, such hot-melt adhesives have the following deficiencies:they are low in initial adhesion (tackiness); they exhibit poor adhesiveperformances at low temperatures; and they show poor adhesion toolefinic polymers such as polyethylene and polypropylene.

The prior art has attempted to enhance adhesion of such olefinicpolymers to low-polarity adherends. An hot-melt adhesive composition(Japanese Patent Laying-Open No. Sho 54-91540) is proposed including ablock copolymer consisting of conjugated diolefiniccopolymer/monovinyl-substituted aromatic compound, an ethylene-vinylacetate copolymer, an ethylenic resin, a phenolic resin and a tackifyingresin. Also proposed is a hot-melt adhesive composition (Japanese PatentLaying-Open No. Sho 54-127441) prepared by adding a liquid rubber havinga specific molecular weight and a tackifying resin to an ethylene-vinylacetate copolymer.

However, the hot-melt adhesive compositions disclosed in Japanese PatentLaying-Open Nos. Sho 54-91540 and Sho 54-127441 both contain a componenthaving a conjugated double bond and thus exhibit unsatisfactory resultsin terms of resistance to deterioration by light and heat.

Acrylic hot-melt adhesives have been developed as materials havingsuperior weather and solvent resistance compared to rubber adhesives andused in various uses. One example of such acrylic hot-melt adhesivecompositions is disclosed in Japanese Patent Laying-Open No. Sho59-75975.

Since this acrylic hot-melt adhesive composition comprises an alkyl(meth)acrylate ester and a functional polymer (macromer), it has beendifficult to impart well-balanced hot-melt and cohesive propertiesthereto. That is, such a composition when used as a hot-melt adhesivesuffers from the following deficiencies. The composition, when exposedto high temperature over 60° C., tends to flow and move across theapplication area. If its cohesive property is enhanced to prevent such aflow, its application becomes difficult as a result of the excessivelyincreased melt viscosity.

It is an object of the present invention to provide an acrylic copolymerwhich contains polymeric portions having different polarities or glasstransition temperatures, which permits easy selection of combinations ofthose polymeric portions having different polarities or glass transitiontemperatures, which permits a broad design freedom and which isapplicable for various uses.

It is another object of the present invention to provide an acrylicpressure-sensitive adhesive composition which is comprised principallyof the acrylic copolymer in accordance with the present invention andwhich shows good adhesion to an adherend regardless of its polaritylevel.

It is a further object of the present invention to provide an acrylicpressure-sensitive adhesive tape or sheet which can solve theabove-described problems encountered in the prior art, i.e., whichexhibits good adhesive properties and properly-reconciled removabilityand adherend non-staining properties and which is also suitablyapplicable for uses that require resistance to weather and light.

It is a further object of the present invention to provide an acrylichot-melt adhesive composition which exhibits good adhesive properties.

DISCLOSURE OF THE INVENTION

A first invention of the present application is an acrylic copolymercharacterized as being prepared via copolymerization of (a) an alkylacrylate ester containing 1-14 carbon atoms in the alkyl, (b) anolefinic polymer or copolymer terminally modified by a free-radicallypolymerizable unsaturated double bond, and (c) a polymer terminallymodified by a free-radically polymerizable unsaturated double bond andhaving a number average molecular weight of 2,000-30,000 and a glasstransition temperature of at least 30° C.

A second invention is an acrylic copolymer characterized as beingprepared by grafting a polymer (e) to an acrylic copolymer made viacopolymerization of (a) an alkyl (meth)acrylate ester containing 1-14carbon atoms in the alkyl, (d) a polymerizable monomer containing onetype of functional group selected from carboxyl, hydroxyl, epoxy andisocyanate and (b) an olefinic polymer or copolymer modified terminallywith a free-radically polymerizable unsaturated double bond. The polymer(e) has at its one end one type of functional group reactive with thefunctional group in the polymerizable monomer (d) and has a numberaverage molecular weight of 2,000-30,000 and a glass transitiontemperature of at least 30° C.

A third invention of the present application is an acrylic copolymercharacterized as being prepared by grafting an olefinic polymer orcopolymer (f) to an acrylic copolymer made via copolymerization of (a)an alkyl (meth)acrylate ester containing 1-14 carbon atoms in the alkyland (d) a polymerizable monomer containing one type of functional groupselected from carboxyl, hydroxyl, epoxy and isocyanate. The olefinicpolymer or copolymer (f) has at its one end one type of functional groupreactive with the functional group in the polymerizable monomer (d).

A fourth invention of the present application is an acrylic copolymercharacterized as being prepared by grafting an olefinic polymer orcopolymer (f) to an acrylic copolymer made via copolymerization of (a)an alkyl (meth)acrylate ester containing 1-14 carbon atoms in the alkyl,(d) a polymerizable monomer containing one type of functional groupselected from carboxyl, hydroxyl, epoxy and isocyanate and (c) a polymerterminally modified by a free-radically polymerizable unsaturated doublebond and having a number average molecular weight of 2,000-30,000 and aglass transition temperature of at least 30° C. The olefinic polymer orcopolymer (f) has at its one terminal one type of functional groupreactive with the functional group in the polymerizable monomer (d).

A fifth invention is an acrylic copolymer characterized as beingprepared by the following first and second steps.

In the first step, a compound (I) containing a free-radicallypolymerizable unsaturated double bond and a peroxide bond in a molecule,an alkyl (meth)acrylate ester (a) containing 1-14 carbon atoms in thealkyl and an olefinic polymer or copolymer (b) terminally modified by afree-radically polymerizable unsaturated double bond are allowed toundergo free-radical polymerization, with the aid of a photoinitiator,in the temperature range where the compound (I) is not caused todecompose. In the second step, a polymerizable monomer component (II)which differs composition from the polymerizable monomer components sedin the preceding free-radical polymerization is allowed to undergofree-radical polymerization, under the presence of the product of thepreceding free-radical polymerization, in the temperature range wherethe compound (I) is caused to decompose.

In the preparation of the acrylic copolymers in accordance with thefirst, second and fifth inventions, an ethylene-butylene randomcopolymer or a propylene polymer terminally modified by a free-radicallypolymerizable unsaturated double bond may preferably be used as theolefinic polymer or copolymer (b).

In the second invention, it is preferred that the functional group inthe polymerizable monomer (d) is an epoxy group and the functional groupin the polymer (e) is a carboxyl group.

For the acrylic copolymers in accordance with the third and fourthinventions, it is preferred that the functional group in thepolymerizable monomer (d) is a carboxyl group. In the fourth invention,preferably, the functional group in the olefinic polymer (c) is an epoxygroup.

For the acrylic copolymer in accordance with the fifth invention, it ispreferred that the polymerizable monomer component (II) used in thesecond step has a glass transition temperature of at least 20° C.

The acrylic pressure-sensitive adhesive composition in accordance withthe present invention is characterized as being comprised principally ofany of the acrylic copolymers in accordance with the first through fifthinventions. In this case, preferably, a hydrogenated petroleum resin mayfurther be included.

In accordance with a further aspect of the present invention, an acrylicpressure-sensitive adhesive tape or sheet is provided which isfabricated by integrating, via coextrusion, a polyolefinic substrate anda pressure-sensitive adhesive layer comprised of the acrylicpressure-sensitive adhesive composition in accordance with the presentinvention.

Also provided in accordance with a further aspect of the presentinvention is an acrylic hot-melt adhesive composition comprisedprincipally of any of the acrylic copolymers in accordance with thefirst through fifth inventions.

The present invention is below described in detail.

(First Invention)

In the first invention, examples of useful alkyl (meth)acrylate esters(a) containing 1-14 carbon atoms in the alkyl include methyl(meth)acrylate, ethyl acrylate, n-propyl (meth)acrylate, isopropyl(meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate,t-butyl (meth)acrylate, cyclohexyl methacrylate, n-octyl (meth)acrylate,isooctyl acrylate, 2-ethylhexyl (meth)acrylate, isononyl acrylate andlauryl (meth)acrylate.

In the present application, (meth)acryl is used to represent acryl andmethacryl collectively.

The above-listed alkyl (meth)acrylate esters (a) may be used alone or incombination.

The aforementioned olefinic polymer or copolymer (b) terminally modifiedby a free-radically polymerizable unsaturated double bond for use in thefirst invention is not particularly specified, so long as it has adouble bond copolymerizable with the other polymerizable monomer andalso has a polymer structure composed of repeating olefinic skeletons.The double bond copolymerizable with the other polymerizable monomer, asused herein, refers to a free-radically polymerizable unsaturated doublebond. Examples of functional groups having such an unsaturated doublebond include a vinyl, (meth)acryloyl, allyl group and the like.

The polymer structure composed of repeating olefinic skeletons can beexemplified by a structure composed of repeating ethylene-butyleneskeletons or a polymer structure composed of repeating propyleneskeletons, i.e., a propylene polymer. A specific example of the olefinicpolymer or copolymer (b) is manufactured by Shell Chemical and marketedin the trade as KRATON LIQUID Polymer L-1253.

The polymer (c) terminally modified by a free-radically olymerizableunsaturated double bond and having a number average molecular weight of2,000-30,000 and a glass transition temperature of at least 30° C., foruse in the first invention, is not particularly specified, so long as ithas a double bond copolymerizable with other polymeric monomers and hasa number average molecular weight of 2,000-30,000 and a glass transitiontemperature of at least 30° C. As described earlier in explaining theolefinic polymer or copolymer (b), the double bond copolymerizable withother polymeric monomer refers to a free-radically polymerizableunsaturated double bond. Examples of functional groups having such anunsaturated double bond include a vinyl, (meth)acryloyl and allyl group.

Preferred for use as the olefinic polymer or copolymer (b) is anethylene-butylene copolymer or propylene polymer each terminallymodified by a free-radically polymerizable unsaturated double bond.

A specific example of the polymer (c) is manufactured by Toa Gosei Chem.Co., Ltd. and marketed in trade as AA-6.

In the first invention, besides alkyl (meth)acrylate ester (a), olefinicpolymer or copolymer (b) and polymer (c), a vinyl monomer may further beallowed to participate in the copolymerization to control the glasstransition temperature or polarity of the resulting acrylic copolymer orto introduce a functional group thereinto. Examples of copolymerizablevinyl monomers include styrenic monomers represented by α-methylstyrene, vinyl toluene and styrene; vinyl ether monomers represented bymethyl vinyl ether, ethyl vinyl ether and isobutyl vinyl ether;unsaturated carboxylic acids or alkyl carboxylate esters such as fumaricacid, monoalkyl fumarate ester, dialkyl fumarate ester, maleic acid,monoalkyl maleate ester, dialkyl maleate ester, itaconic acid andmonoalkyl itaconate ester; (meth)acrylo-nitrile, butadiene, isoprene,vinyl chloride, vinylidene chloride, vinyl acetate, vinyl ketone,vinylpyrrolidone, vinylpyridine, (meth)acrylamide, vinylcarbazole andthe like.

The acrylic copolymer in accordance with the first invention, if itsweight average molecular weight is excessively low, may fail to exhibitpolymeric properties. On the other hand, if its weight average molecularweight is excessively high, the acrylic copolymer while produced may beincreased in viscosity to result in low productivity. Accordingly, theweight average molecular weight of the acrylic copolymer is preferablycontrolled to fall within the range of 10,000-4,000,000, more preferablywithin the range of 200,000-2,000,000.

The acrylic copolymer in accordance with the first invention can beproduced by various processes including solution polymerization and bulkpolymerization and is readily obtainable, in general, by allowing thealkyl (meth)acrylate ester (a), olefinic polymer or copolymer (b) andpolymer (c) to dissolve in a suitable solvent such as ethyl acetate andthen subjecting the mixture to solution polymerization using apolymerization initiator.

Other applicable method involves providing a solvent-free liquid mixturecontaining the alkyl (meth)acrylate ester (a), olefinic polymer orcopolymer (b), polymer (c) and photoinitiator and then irradiating themixture with an ultraviolet light to initiate polymerization thereof ina nitrogen or other inert atmosphere.

The blending proportions of the alkyl (meth)acrylate ester (a), olefinicpolymer or copolymer (b) and polymer (c) in the first invention will benow described.

The reduced amount of the olefinic polymer or copolymer (b) results inthe failure to impart desired properties to the acrylic copolymer. Onthe other hand, the excessive amount thereof lowers compatibility toresult in the reduced utility. Accordingly, the olefinic polymer orcopolymer (b) is preferably contained in the amount of 5-100 parts byweight, more preferably 10-50 parts by weight, based on 100 parts byweight of the alkyl (meth)acrylate ester (a).

The excessive reduction in amount of the polymer (c) results in thefailure to impart polymeric cohesion to the acrylic copolymer, while theexcessive increase in amount thereof causes gellation to result in thereduced utility. Accordingly, the polymer (c) is preferably contained inthe amount of 5-100 parts by weight, more preferably 10-30 parts byweight, based on 100 parts by weight of the alkyl (meth)acrylate ester(a).

(Second Invention)

The alkyl (meth)acrylate ester (a) containing 1-14 carbon atoms in thealkyl for use in the second invention is similar in type to that for usein the first invention. Accordingly, its detail is omitted here byreferring to the description given in explaining the first invention.

The polymerizable monomer (d) containing one type of functional groupselected from carboxyl, hydroxyl, epoxy and isocyanate is notparticularly specified, so long as it is a polymerizable monomercontaining any one type of those functional groups.

Examples of carboxyl-containing polymerizable monomers (d) includecarboxylic acids such as (meth)acrylic acid, itaconic acid, crotonicacid, maleic acid (anhydride) and fumaric acid (anhydride);carboxyl-containing (meth)acrylate esters such as carboxyethyl acrylateand the like. Examples of hydroxyl-containing polymerizable monomers (d)include 2-hydroxyethyl (meth)acrylate, hydroxypropyl acrylate,4-hydroxybutyl acrylate, caprolactone-modified (meth)acrylate,polyoxy-ethylene oxide-modified (meth)acrylate and the like.

Examples of epoxy-containing polymerizable monomers (d) include anglycidyl methacrylate ester and the like. Examples ofisocyanate-containing polymerizable monomers (d) include methacryloylisocyanate and the like.

The olefinic polymer or copolymer (b) terminally modified with afree-radically polymerizable unsaturated double bond for use in thesecond invention is similar in type to that used in the first invention.Accordingly, its detail is omitted here by referring to the descriptiongiven in explaining the first invention.

In the second invention, the olefinic polymer or copolymer (b)preferably comprises an ethylene-butylene random copolymer or propylenepolymer, terminally modified with a free-radically polymerizableunsaturated double bond. More preferably, the olefinic polymer orcopolymer (b) comprises the above ethylene-butylene random copolymer orpropylene polymer, the polymerizable monomer (d) comprises a monomercontaining an epoxy as a functional group, and the polymer (e) comprisesa polymer containing a carboxyl as a functional group.

In the second invention, the acrylic copolymer (X-1) prepared viacopolymerization of the aforementioned alkyl meth)acrylate ester (a),polymerizable monomer (d) and olefinic polymer or copolymer (b) is used.This acrylic copolymer may further be copolymerized with the other vinylmonomer to control its glass transition temperature or polarity or tointroduce other functional group, as similar to the case of the firstinvention. Such a copolymerizable vinyl monomer is similarly in type tothat used in the first invention, and accordingly its detail is omittedhere by referring to the description given in the first invention.

In the second invention, the polymer (e) is further grafted to theacrylic copolymer (X-1). The polymer (e) has at its one end one type offunctional group reactive with the functional group in the polymerizablemonomer (d) and has a number average molecular weight of 2,000-30,000and a glass transition temperature of at least 30° C.

Examples of polymers (e) containing at its one end one type offunctional group reactive with the functional group in the polymerizablemonomer (d) and having a number average molecular weight of 2,000-30,000and a glass transition temperature of at least 30° C. includehomopolymers or copolymers derived from styrene, methyl methacrylateester, α-methylstyrene, o-methylstyrene, p-methylstyrene, acrylonitrile,vinyl acetate and the like. These may be used alone or in combination.Alternatively, the polymer (e) may be obtained by allowing apolymerizable monomer containing such a functional group as styrene,methyl ethacrylate ester, α-methylstyrene, o-methylstyrene,p-ethylstyrene, acrylo-nitrile or vinyl acetate to undergoopolymerization with the other monomer copolymerizable with theaforementioned polymerizable monomer, with the use of a chain transferagent such as mercaptoethanol if desired to introduce a hydroxyl groupat one end of the polymer, or alternatively, mercaptoacetic acid orpropionic acid if desired to introduce a carboxyl group at one end ofthe polymer.

If the content of the polymer (e) having a functional group at its oneend is excessively low, in an exemplary case where the acrylic copolymerin accordance with the second invention is utilized as apressure-sensitive adhesive, the cohesion of the pressure-sensitiveadhesive may become too low to obtain satisfactory heat resistance. Bycontrast, if its content is excessively high, the pressure-sensitiveadhesive itself may become excessively hard to reduce its adhesiveproperties. It is accordingly preferred that 5-100 parts by weight ofthe polymer (e) is grafted to 100 part by weight of the acryliccopolymer X-1).

As similar to the acrylic polymer in accordance with the firstinvention, the acrylic polymer in accordance with the second invention,if its weight average molecular weight is excessively low, may fail toexhibit characteristics as a polymer. On the other hand, if its weightaverage molecular weight is excessively high, the acrylic copolymerwhile produced may be increased in viscosity to result in lowproductivity. Accordingly, the weight average molecular weight of theacrylic copolymer is preferably controlled to fall within the range of10,000-4,000,000, more preferably within the range of 200,000-2,000,000.

Also in the second invention, polymerization of the acrylic copolymer(X-1) can be achieved by varous techniques including solutionpolymerization, bulk polymerization, suspension polymerization andemulsion polymerization. The general method used to readily obtain theacrylic copolymer involves allowing the alkyl (meth)acrylate ester (a)and other essential ingredients, optionally with additives, to dissolvein a suitable solvent, e.g., ethyl acetate, and then subjecting themixture to solution polymerization using a polymerization initiator.

Also in the second invention, a conventional technique can be utilizedto graft the polymer (e) to the acrylic copolymer (X-1).

In the preparation of the acrylic polymer in accordance with the secondinvention, if the blending proportion of the polymerizablem monomer (d)is excessively low, a desired graft effect may not be obtained. On theother hand, if it is excessively high, the acrylic polymer may beincreased in polarity to an excessive extent. It is thus preferred thatthe polymerizable monomer (d) is contained in the range of 0.1-10 partsby weight, more preferably in the range of 1-5 parts by weight, based on100 parts by weight of the alkyl (meth)acrylate ester (a).

If the blending proportion of the olefinic polymer or copolymer (b) isexcessively low, desired properties may not be obtained. On the otherhand, if it is excessively high, the compatibility may be lowered toresult in the reduced utility. Accordingly, the olefinic polymer orcopolymer (c) is preferably contained in the amount of 5-100 parts byweight, more preferably 10-50 parts by weight, based on 100 parts byweight of the alkyl (meth)acrylate ester (a)

(Third Invention)

The alkyl (meth)acrylate ester (a) containing 1-14 carbon atoms in thealkyl and the polymerizable monomer (d) containing one type offunctional group selected from carboxyl, hydroxyl, epoxy and isocyanate,for use in the third invention are similar in types to those used in thefirst and second inventions. Accordingly, the preceding descriptionsthereon can be referred to.

In the third invention, the aforementioned alkyl (meth)acrylate ester(a) and polymerizable monomer (d) are allowed to undergocopolymerization. As similar to the first or second invention, othervinyl monomer may further be allowed to participate in thecopolymerization to control a glass transition temperature or polarityof the resulting acrylic copolymer or to introduce another functionalgroup thereinto. The detail of the other vinyl monomer is omitted hereby referring to the description given in explaining the first invention.

In the third invention, the polymerizable monomer (d) preferablycontains a carboxyl group.

More preferably, the polymerizable monomer (d) contains a carboxyl groupand the olefinic polymer (c) contains an epoxy group.

In the third invention, the olefinic polymer or copolymer (f) having atits one end one type of functional group reactive with a functionalgroup in the polymerizable monomer (d) is grafted to the acryliccopolymer (X-2) made via copolymerization of at least the aforementionedalkyl (meth)acrylate ester (a) and polymerizable monomer (d).

The olefinic polymer or copolymer (f) is not specified particularly, solong as it contains at its one end one type of functional group reactivewith a functional group in the polymerizable monomer (d) and has anumber average molecular weight and glass transition temperature withinthe above-specified resepective ranges. Examples of such olefinicpolymers or copolymers (f) include those having a polymer structurecomposed of repeating ethylene-butylene skeletons. specific example ofsuch an olefinic polymer or copolymer manufactured by Shell Chemical andmarketed in trade as ATON LIQUID Polymer EKP-207.

For the same reasons as provided in the first and second inventions, itis preferred that the acrylic copolymer in accordance with the thirdinvention has a eight average molecular weight within the range asspecified above for the acrylic polymers in accordance with the firstand second inventions.

In the preparation of acrylic copolymers in accordance with the thirdinvention, various techniques can be utilized to polymerize the acryliccopolymer (X-2) and graft the olefinic polymer (f) to the acryliccopolymer (X-2), as similar to the second invention.

In the third invention, if the polymerizable monomer (d) content isexcessively low, a desired graft effect may not be obtained. If it isexcessively high, the acrylic polymer may be increased in polarity to anexcessive extent. Accordingly, the polymerizable monomer (d) ispreferably incorporated in the range of 0.1-10 parts by weight, morepreferably in the range of 1-5 parts by weight, based on 100 parts byweight of the alkyl (meth)acrylate ester (a).

If the olefinic polymer (f) content is excessively low, desiredproperties may not be obtained. On the other hand, if it is excessivelyhigh, the compatibility may be lowered result in the reduced utility.Accordingly, the olefinic polymer (f) is preferably added in the amountof 5-100 arts by weight, more preferably 10-50 parts by weight, based on100 parts by weight of the acrylic copolymer (X-2).

(Fourth Invention)

The acrylic copolymer (X-3) for use in the preparation of the acryliccopolymer in accordance with the fourth invention is prepared viacopolymerization of (a) an alkyl (meth)acrylate ester containing 1-14carbon atoms in the alkyl, (d) a polymerizable monomer containing onetype of functional group selected from carboxyl, hydroxyl, epoxy andisocyanate and (c) a polymer terminally modified by a free-radicallypolymerizable unsaturated double bond and having a number averagemolecular weight of 2,000-30,000 and a glass transition temperature ofat least 30° C. These alkyl (meth)acrylate ester (a), polymerizablemonomer (d) and polymer (c) are similar to those used in the first andsecond inventions. Accordingly, their details are omitted here byreferring to the descriptions given in explaining the first and secondinventions.

In the fourth invention, the acrylic copolymer (X-3) can also be usedwhich is made by further participation of the other vinyl monomer in thecopolymerization, as stated in the first invention.

In the fourth invention, the olefinic polymer or copolymer (f) having atits one end one type of functional group reactive with a functionalgroup in the polymerizable monomer (d) is grafted to the acryliccopolymer (X-3). The olefinic polymer or copolymer (f) is similar tothat used in the third invention. Accordingly, its detail is omittedhere by referring to the description given in explaining the thirdinvention.

For the same reasons as provided in the first and second inventions, itis desired that the acrylic copolymer in accordance with the fourthinvention has a weight average molecular weight within the range asabove specified for the acrylic polymers in accordance with the firstand second inventions.

In the preparation of acrylic copolymers in accordance with the thirdinvention, various techniques can be utilized to polymerize the acryliccopolymer (X-3) and graft the olefinic polymer or copolymer (f) to theacrylic copolymer (X-3), as similar to the second invention.

In the fourth invention, if the blending proportion of the polymerizablemonomer (d) is excessively low, a desired graft effect may not beobtained. If it is excessively high, the acrylic polymer may beincreased in polarity to an excessive extent. Accordingly, thepolymerizable monomer (d) is preferably incorporated within the range of0.1-10 parts by weight, more preferably within the range of 1-5 parts byweight, based on 100 parts by weight of the alkyl (meth)acrylate ester(a).

If the blending proportion of the polymer (c) is excessively low, goodcohesion as a graft effect may not be obtained. On the other hand, if itis excessively high, the acrylic copolymer may be increased in hardnessto an excessive extent. It is accordingly preferred that the polymer (c)is incorporated in the amount of 5-100 parts by weight, more preferably10-30 parts by weight, based on 100 part by weight of the alkyl(meth)acrylate ester (a).

Also in the fourth invention, if the blending proportion of the olefinicpolymer (f) is excessively low, desired properties may not be obtained.On the other hand, if it is excessively high, the compatibility may belowered to result in the reduced utility. Accordingly, the olefinicpolymer (f) is preferably added in the amount of 5-100 parts by weight,more preferably 10-50 parts by weight, based on 100 parts by weight ofthe acrylic copolymer (X-3).

(Fifth Invention)

As stated earlier, the first and second steps are utilized to preparethe acrylic copolymer in accordance with the fifth invention. In thefirst step, the compound (I) containing a free-radically polymerizableunsaturated double bond and a peroxide bond in a molecule, alkyl(meth)acrylate ester (a) containing 1-14 carbon atoms in the alkyl andolefinic polymer or copolymer (b) terminally modified by afree-radically polymerizable unsaturated double bond are allowed toundergo free-radical polymerization, with the aid of a photoinitiator,in the temperature range where the compound (I) is not caused todecompose.

The compound (I) is not particularly specified in type, so long as itcontains, in a molecule, a free-radically polymerizable unsaturateddouble bond and a peroxide bond which when heated decompose to generateradicals. The meaning of the free-radically polymerizable unsaturatedbond is described earlier. Examples of functional groups having such afree-radically polymerizable unsaturated double bond include a vinyl,(meth)acryloyl, allyl group and the like.

Peroxides having a peroxide bond can be classified into the followinginitiator groups according to the ease of radical generation;high-temperature initiators suitable for use at temperatures over 100°C., (medium-temperature) initiators suitable for use at temperaturesbetween 40° C. and 100° C., low-temperature initiators suitable for useat temperatures between −10° C. and 40° C., and ultralow-temperatureinitiators suitable for use at temperatures below −10° C. (Chemistry ofPolymer Synthesis, revised edition, Takayuki Ohtsu). Preferred for usein the present invention are those compounds classified as the medium-to high-temperature initiators suitable for use at temperatures of 40°C. and over. The use of such compounds results in the efficientproduction of graft polymers. As an example of such a compound (I),t-butyl peroxyallyl carbonate (PEROMER AC, name used in trade andmanufactured by NOF Corporation) is sold in the market.

The process used to achieve free-radical polymerization in the firststep is not particularly specified, and may be chosen from variouspolymerization processes including bulk polymerization, solutionpolymerization, suspension polymerization and emulsion polymerization.

The temperature range, in the first step, where the compound (I) is notcaused to decompose can be set on the basis of a 10 hour half-lifetemperature which is generally used as an indication of a decompositionrate of an organic peroxide. It is desired that the temperature be setwithin the range that is preferably 20° C., more preferably 30° C.,lower than the 10 hour half-life temperature of the compound (I) used.If the temperature is set at an excessively high value, decomposition ofthe compound (I) may be caused to occur in the first step. This causesgellation to result in the failure to obtain the acrylic copolymerefficiently.

The photoinitiator for use in the first step must be the one which doesnot generate free-radicals via thermal decomposition. Examples of suchphotoinitiators include acetophenones such as4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone (product name:DAROCUR 2959, manufactured by Merck & Co. Inc.),α-hydroxy-α,α′-dimethylacetophenone (product name: DAROCUR 1173,manufactured by Merck & Co. Inc.), methoxy-acetophenone,2,2-dimethoxy-2-phenyl-acetophenone; benzoin ethers such as benzoinethyl ether and benzoin isopropyl ether; and ketals such as benzyldimethyl ketal. Other examples includebis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphineoxide (productname: BDTPO, manufactured by Ciba Geigy Co.), halogenated ketones,acylphosphine oxides, acylphosphinates and the like.

The alkyl (meth)acrylate ester (a) and olefinic polymer or copolymer (b)for use in the first step are similar to those described in the firstand third inventions. Their details are accordingly omitted here byreferring to the preceding descriptions given in explaining the firstand third inventions.

Also in the first step, other vinyl monomer than the aforementionedalkyl (meth)acrylate ester (a), olefinic polymer or copolymer (b) andcompound (I) may further be allolwed to participate in thecopolymerization. The vinyl monomers described in the first inventionare also useful for the other vinyl monomer.

In the second step, a polymerizable monomer component (II) which deffersin composition from the polymerizable monomer components used in thepreceding free-radical polymerization is allowed to undergo free-radicalpolymerization, under the presence of the product from the precedingfree-radical polymerization, in the temperature range wheredecomposition of the compound (I) is caused to occur.

The second step temperature range where decomposition of the compound(I) occurs can be set in a similar manner to the first step temperaturerange where decomposition of the compound (I) does not occur, i.e., onthe basis of the 10 hour half-life temperature. In the second step, itis desired that the temperature be set within the range that does notfall preferably below (10 hour half-life temperaure of the compound(I)—30)° C., more preferably below (10 hour half-life temperature of thecompound (I)—20)° C. If the set temperature is excessively low, thefree-radical polymerization in the second step may not be initiatedefficiently upon exposure to heat. This reduces the graft efficiency ofthe resulting acrylic copolymer.

Examples of polymerizable monomer components (II) having glasstransition temperatures of not below 20° C. for use in the preparationof copolymers include styrene, methyl methacrylate ester, α-methylstyrene, o-methyl styrene, p-methyl styrene, acrylonitrile, vinylacetate and the like. The use of methyl methacrylate ester and styreneis preferred.

For the same reasons as provided in the first and second inventions, itis desired that the acrylic copolymer in accordance with the fifthinvention has a weight average molecular weight within the range asabove specified for the acrylic polymers in accordance with the firstand second inventions.

For the acrylic copolymer in accordance with the fifth invention, if theblending proportion of the compound (I) is excessively low, the reducedgraft effect may result. If it is excessively high, a proportion of thecompound (I) that does not participate in the polymerization mayincrease. Accordingly, the compound (I) is preferably incorporated inthe amount of 0.01-10 parts by weight, more preferably 0.1-5 parts byweight, based on 100 part by weight of the alkyl (meth)acrylate ester(a).

Also, if a blending proportion of the olefinic polymer or copolymer (b)is excessively low, desired properties may not be obtained. On the otherhand, if it is excessively high, the compatibility may be lowered toresult in the reduced utility. Accordingly, the olefinic polymer orcopolymer (b) is preferably incorporated in the amount of 5-100 parts byweight, more preferably 10-50 parts by weight, based on 100 parts byweight of alkyl (meth)acrylate ester (a).

In the fifth invention, if a blending proportion of the polymerizablemonomer component (II) is excessively low, good cohesion as a grafteffect may not be obtained. If it is excessively high, the resultingacrylic copolymer may be increased in hardness to an excessive extent.Accordingly, the polymerizable monomer component (II) is preferablyadded in the amount of 5-100 parts by weight, more preferably 10-30parts by weight, based on 100 part by weight of the alkyl (meth)acrylateester (a).

(Acrylic Pressure-Sensitive Adhesive Composition)

The acrylic pressure-sensitive adhesive composition in accordance withthe present invention is characterized as being comprised primarily ofany of acrylic copolymers in accordance with the above-described firstthrough fifth inventions. That is, since the acrylic copolymer accordingto any one of the first through fifth inventions has a graft structurewherein a lower-polariy polymer branches off from a higher-polaritycopolymer backbone comprised primarily of an alkyl (meth)acrylate ester,the pressure-sensitive adhesive composition comprised primarily of suchan acrylic copolymer exhibits superior adhesive performances relative tosurfaces of adherends varied in polarity over a wide range, includinghigh-polarity metal adherends and low-polarity plastic adherends.

Preferably, a hydrogenated petroleum resin, other than the acryliccopolymer, may further be incorporated in the acrylic pressure-sensitiveadhesive composition.

The hydrogenated petroleum resin refers to an alicyclic petrolium resinwhich results from hydrogenation of a C9 petroleum resin obtained viacationic polymerization of a C9 fraction derived from naphtha crackingor from hydrogenation of a petroleum resin obtained via thermalpolymerization of a C5 fraction comprised chiefly of cyclopentadiene orC5 fraction derived dicyclopentadiene.

The C9 fraction contains such polymerizable components asα-methylstyrene, vinyltoluene, vinylxylene, propenyl-benzene, indene andmethylindene, and is generally available in the form of a mixture ofthose polymeric components.

Such a petroleum resin is generally hydrogenated under the conditions of200-300° C. and 10-300 kg/cm², using a hydrogenation catalyst asillustrated by metals such as nickel, palladium, cobalt, ruthenium,platinum and rhodium and their mixtures.

The hydrogenated petroleum resin for use in the present inventionpreferably has a number average molecular weight of 500-1,000 and asoftening point of 60-150° C. Preferably, it is a 100% hydrogenatedresin, i.e., a so-called completely hydrogenated product. Such a resinis commercially available, for example, from Arakawa ChemicalIndustries, Ltd. under the trade designation of ARKON P140.

Although not particularly specified, the hydrogenated petroleum resin ispreferably incorporated in the amount of 5-50 parts by weight, based on100 parts by weight of the acrylic copolymer in accordance with any ofthe first through fifth inventions. If the amount is below 5 parts byweight, desired adhesion to olefin or oil surface may not result. If itexceeds 50 parts by weight, its compatibility with the acrylic copolymermay drop to result in the reduced stability of a resultingpressure-sensitive adhesive.

In the case where the pressure-sensitive adhesive composition inaccordance with the present invention is used to form apressure-sensitive tape or sheet, it may be applied, in the form of alayer, to one surface of a substrate, or alternatively, to both surfacesthereof to provide a so-called double coated tape. In the case of thepressure-sensitive adhesive double coated tape, the pressure-sensitiveadhesive composition in accordance with the present invention may beapplied to provide a pressure-sensitive adhesive layer on at least onesurface of the tape.

The material used to form the substrate may be suitably chosen frompaper; non-woven fabric; plastic films such as made of polyesters andpolyolefins; and plastic foams such as derived from polyolefins,polyurethanes, polychloroprene, soft vinyl polychloride and acrylicresins. Alternatively, the substrate may be excluded to provide aself-supporting pressure-sensitive adhesive sheet.

(Other Additives)

The acrylic copolymer and acrylic pressure-sensitive adhesivecomposition in accordance with the present invention may further containa crosslinking agent within the range that does not interfere with thepurposes of the present invention to insure increased cohesion. Examplesof such crosslinking agents are conventionally known in the art andinclude isocyanate, aziridine and epoxy crosslinking agents. Electronbeam or other radiation crosslinking may be carried out.

When necessary, the acrylic copolymer and acrylic pressure-sensitiveadhesive composition in accordance with the present invention mayfurther contain various additives conventionally known in the art,including a tackifier, plasticizer, softener, filler, stabilizer,anti-oxidant, pigment and dye, for example.

(Acrylic Pressure-Sensitive Tape or Sheet)

In accordance with a further aspect of the present invention, an acrylicpressure-sensitive tape or sheet is provided comprising a polyolefinicsubstrate and a pressure-sensitive adhesive layer comprised of theacrylic pressure-sensitive adhesive composition in accordance with thepresent invention as described above, which are integrated viacoextrusion.

Any polyolefinic substrate may be used if it takes the form of aflexible film or sheet containing ethylene and/or propylene, e.g.,polyethylene and/or polypropylene, as a primary constituent.

Examples of polyethylenes include high density polyethylene (HDPE),medium density polyethylene (MDPE), low density polyethylene (LDPE) andlinear low density polyethylene (LLDPE). These may be copolymerized witha long-chain olefinic monomer such as 1-butene or 1-pentene.

Examples of polypropylenes include random, homo, highly crystalline,block polypropylenes, and other flexible types.

In the acrylic pressure-sensitive tape or sheet in accordance with thepresent invention, the aforementioned polyolefinic substrate andpressure-sensitive adhesive layer are integrated via coextrusion. Thetechnique utilized to integrate them by coextrusion is not particularlyspecified. To illustrate one technique, such a tape or sheet can beobtained by concurrently extruding a polyolefinic substrate material anda pressure-sensitive adhesive layer material from separate extruders andthen coextruding them by using a blown film, T-die or other extrusionprocess.

The acrylic pressure-sensitive adhesive tape or sheet thus obtained viacoextrusion may be irradiated with an electron beam to crosslink theacrylic pressure-sensitive layer or to improve an anchor effect relativeto associated adherends.

Also, an interlayer may be provided between the polyolefinic substrateand acrylic pressure-sensitive adhesive layer to improve anchortherebetween. The resin for use as the interlayer is not particularlyspecified, so long as it is effective to anchor the pressure-sensitiveadhesive layer. Examples of interlayer resins include high-polarityresins such as EEA resins (ethylene-ethyl acrylate copolymers, e.g.,PRIMACOR manufactured by Dow Chemical Company), maleic anhydride addedpolyethylene and epoxy modified polyethylenes. Modified polyethylenes,modified polypropylenes or other modified polyolefins are suitably used.

(Acrylic Hot-Melt Adhesives)

The acrylic hot-melt adhesive provided in accordance with a furtheraspect of the present invention is comprised chiefly of the acryliccopolymer in accordance with any one of the first through fifthinventions. When necessary, the acrylic hot-melt adhesive compositionmay further contain, as auxiliary ingredients, various additivesconventionally known in the art such as a tackifier, plasticizer,softener, anti-oxidant, pigment and dye, for example. Alternatively, thehot-melt adhesive may be comprised solely of the acrylic copolymer.

(Action)

The acrylic copolymers in accordance with the first through fifthinventions have a graft structure in which the aforementioned olefinicpolymer or copolymer (b) and polymer (c) having a high glass transitiontemperature branch off from the copolymer backbone comprised chiefly ofalkyl (meth)acrylate ester (a). Since its polymeric backbone portion iscomprised chiefly of the highly polar alkyl (meth)acrylate ester (a) anddistinguished in polarity from its polymeric branch portions, a suitablepolarity control of the polymeric branch portions results in obtainingan acrylic copolymers containing a higher-polarity backbone portion andlower-polarity branch portions.

Because of inclusion of such polymeric portions having differentpolarities, the acrylic copolymer in accordance with the presentinvention can be used, for example, as an agent for dispersingpolybutadiene rubber in an AS resin (acrylonitrile-styrene copolymerresin) or as an impact modifying resin.

The use of the acrylic copolymer having such polymeric portions withdifferent polarities enables application of resulting pressure-sensitiveadhesives to high-polarity metals, low-polarity plastics and otheradherends without failure to exhibit superior adhesive properties. Thatis, pressure-sensitive adhesives can be provided which are applicable toadherends varied in polarity over a wide range.

In addition, the acrylic copolymers in accordance with the presentinvention have polymeric branch portions of high glass transitiontemperatures in their structures. In the case where the polymericbackbone portion is comprised chiefly of the alkyl (meth)acrylate ester(a) having a low glass transition temperature, the formation of acontinuous phase by the polymeric portions having high glass transitiontemperatures results in provision of the acrylic copolymers which aresuitable for use as high heat-resistant or impact-resistant compounds ortoner resins. On the other hand, the formation of a continuous phase bypolymeric portions having low glass transition temperatures results inthe provision of the acrylic copolymers which are suitable for use inthe preparation of high-strength or high-orientation films, hot-meltadhesives or thermoplastic elastomers.

The acrylic copolymer in accordance with the first invention is a graftcopolymer in which the polymeric backbone portion derived from alkyl(meth)acrylate ester (a) containing 1-14 carbon atoms in the alkyl iscombined with the polymeric branch portion derived from the olefinicpolymer or copolymer (b) or the polymer (c). Accordingly, acryliccopolymers applicable for various uses can be provided by suitablydesigning the polarities and glass transition temperatures of thosepolymeric portions according to the purposes contemplated.

The acrylic copolymer in accordance with the second invention has agraft structure wherein polymeric portions respectively derived from theolefinic polymer copolymer (b) and the polymer (e) branch off from thecopolymer backbone comprised chiefly of the alkyl (meth)acrylate ester(a).

That is, the acrylic copolymer includes a polymeric backbone portioncomprised chiefly of a highly polar alkyl (meth)acrylate ester, assimilar to the acrylic copolymer of the first invention. By renderingany polymeric branch portion less polar, acrylic copolymers can beprovided comprising a combination of polymeric portions having differentpolarities. Thus, suitably selecting combinations of such polymericportions results in acrylic copolymers applicable for various uses, assimilar to the first invention.

The acrylic copolymer in accordance with the third invention has a graftstructure in which the olefinic polymer (f) branches off from apolymeric backbone portion made via copolymerization of alkyl(meth)acrylate ester (a) and polymerizable monomer (d) and comprisedchiefly of alkyl (meth)acrylate ester (a).

That is, it has a polymeric backbone portion comprised chiefly of ahighly polar alkyl (meth)acrylate ester and also has a polymeric branchportion lower in polarity than the polymeric backbone portion, assimilar to the acrylic copolymer of the first invention. Acryliccopolymers are thus provided comprising combinations of polymericportions of different polarities. Accordingly, suitably selectingcombinations of such polymeric portions results in acrylic copolymerswhich are applicable for various uses, as similar to the firstinvention.

Similarly, in the acrylic copolymer in accordance with the fourthinvention, the olefinic polymer or copolymer (f) is grafted to branchoff from the copolymer backbone portion made via copolymerization of thealkyl (meth)acrylate ester (a), polymerizable monomer (d) and polymer(c) and comprised chiefly of alkyl (meth)acrylate ester (a).

That is, the acrylic copolymer includes the highly polar polymericbackbone portion and the polymeric branch portion lower in polarity thanthe polymeric backbone portion, as similar to the first invention.Acrylic copolymers are accordingly provided having a combination ofpolymer portions having different polarities. Thus, suitably selectingcombinations of such polymeric portions results in acrylic copolymerswhich are applicable for various uses, as similar to the firstinvention.

Similarly, the acrylic copolymer in accordance with the fifth inventionhas a graft structure in which the polymeric portion obtained viapolymerization of the polymerizable monomeric component (II) branchesoff from a copolymer backbone portion made via copolymerization of thealkyl (meth)acrylate ester (a), olefinic polymer or copolymer (b) andcompound (I).

That is, the acrylic copolymer contains a polymeric backbone portioncomprised chiefly of the highly polar alkyl (meth)acrylate ester, assimilar to the first invention. By rendering the polymeric branchportion less polar, acrylic copolymers can be provided comprising acombination of polymeric portions having different polarities. Thus,suitably selecting combinations of such polymeric portions results inacrylic copolymers applicable for various uses, as similar to the firstinvention.

The acrylic pressure-sensitive adhesive composition in accordance withthe present invention is comprised chiefly of any of the acryliccopolymers in accordance with the first through fifth inventions. Thus,selective combination of polymeric portions in the acrylic copolymerresults in adhesive compositions which exhibit high adhesive strengthwith respect to adherends varied in polarity.

Also, the acrylic copolymers in accordance with the first, second andfourth inventions contain the polymer (c) having a glass transitiontemperature of at least 30° C. and are designed to incorporate a polymerbackbone portion comprised mainly of the alkyl (meth)acrylate ester (a)that has a low glass transition temperature. Accordingly, the formationof a continuous phase by polymer portions derived from the polymers (c),(e) that show high glass transition temperatures results in theprovision of acrylic copolymers which have imparted thereto increasedresistance to heat and impact. Such acrylic copolymers are preferred foruse as compounds requiring high resistance to heat and impact or astoner resins. Also, the formation of a continuous phase by polymericportions derived from polymers that show low glass transitiontemperatures results in the provision of acrylic copolymers suitable foruse as films requiring high strength and elongation, hot-meltpressure-sensitive adhesives, thermoplastic elastomers and the like.

Also, the devised combinations of the aforementioned polymeric portionsresults in the acrylic pressure-sensitive adhesive compositions whichhave imparted thereto the heat resistance and low-temperature tackinesswell-balanced at high levels.

In the aforesaid other aspect of the present invention, the acrylicpressure-sensitive adhesive layer consisting of the above-describedacrylic pressure-sensitive adhesive composition is coextruded with thepolyolefinic substrate for integration into an acrylicpressure-sensitive adhesive tape or sheet. Accordingly, such a tape orsheet exhibits good adhesive properties and well-balanced removabilityand non-staining properties with respect to adherends. Further, it isapplicable for such uses that require resistance to weather and light.

Also, the acrylic hot-melt adhesive composition in accordance with thepresent invention is comprised chiefly of the acrylic copolymer inaccordance with the present invention. Accordingly, it shows goodadhesive properties over a wide temperature range. Further, the improvedweather resistance of the adhesive composition and its capability towell-balance melt viscosity and cohesion make it suitable for use in theform of a hot melt.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will be clarified by the following non-limitingexamples.

EXAMPLE 1

141 g of butyl acrylate (hereinafter referred to as BA), 150 g of2-ethylhexyl acrylate (hereinafter referred to as 2EHA), 9 g of acrylicacid (hereinafter referred to as AAc), 0.9 g of 2-hydroxylethyl acrylate(hereinafter referred to as 2HEA), 122.73 g of ethyl acetate and 122.73g of toluene were charged into a 2 liter separable flask equipped with astirrer, cooling condenser, thermometer and nitrogen inlet to provide aliquid-form monomer mixture.

The monomer mixture was bubbled with nitrogen for 20 minutes to removedissolved oxygen, and then elevated in temperature using a water bathwhile stirred at a velocity of 100 rpm.

At the point when the appearance of a reflux liquid was observed, 0.03 gof 1,1-di(t-hexylperoxy)-3,3,5-trimethyl cyclohexane (product name:PERHEXA TMH, manufactured by NOF Corp.) was dissolved in about 1 g ofethyl acetate and then added, as a polymerization initiator, to themonomer mixture to initiate boiling-point polymerization.

After the passage of one hour, 0.05 g of PERHEXA TMH was dissolved inabout 1 g of ethyl acetate and again added to the mixture. After thepassage of 2, 3 and 4 hours from the start of polymerization, 0.06 g,0.3 g and 0.9 g of di(3,5,5-trimethylhexanoyl)peroxide (product name:PEROYL 335, manufactured by NOF Corp.), respectively dissolved in about1 g of ethyl acetate, were added. The boiling-point polymerization wascontinued for 7 hours to obtain an acrylic copolymer.

The acrylic polymer was determined to have a weight average molecularweight of 764,000 and a polydispersity (M_(w)/M_(n)) of 2.6.

Subsequently, 33 g of a 50 wt. % solution of an olefinic polymer havinga terminal epoxy group (product name: KRATON LIQUID Polymer EK-207,manufactured by Shell Chemical Comp.) in toluene was added to 100 g ofthe above-obtained acrylic copolymer and mixed with stirring to obtainan aimed acrylic pressure-sensitive adhesive.

EXAMPLE 2

11 g of a 50% solution of hydrogenated petroleum resin (product name:ARKON P140, manufactured by Arakawa Chemical Industries, Ltd.) intoluene was added to 133 g of the acrylic pressure-sensitive adhesivesolution obtained in Example 1. Thereafter, they were mixed withstirring to obtain an aimed acrylic pressure-sensitive adhesive.

COMPARATIVE EXAMPLE 1

11 g of a 50% solution of hydrogenated petroleum resin (product name:ARKON P140, manufactured by Arakawa Chemical Industries, Ltd.) intoluene was added to 100 g of the acrylic copolymer solution obtained inExample 1. They were subsequently mixed with stirring to obtain an aimedacrylic pressure-sensitive adhesive.

(Fabrication of Pressure-Sensitive Adhesive Tape)

A solution of methylolpropanetolylene diisocyanate trimer adduct inethyl acetate (solids content of 45 wt. %, product of NipponPolyurethane Industry Co., Ltd., product name: CORONATE 45), as acrosslinking agent, was added to the pressure-sensitive adhesivecompositions obtained in Examples 1 and 2 and Comparative Example 1 inthe amount of 2.5 parts by weight, based on 100 parts by weight of therespective acrylic copolymer. After mixed homogeneously, eachcomposition was coated on a surface of a 38 μm thick polyester film(product of Lintec Corporation, product number: #3811) to such athickness that measured 25 μm when dried later. The subsequent drying at110° C. for 5 minutes resulted in obtaining pressure-sensitive tapes.

(Measurement of SP Adhesion)

In accordance with the procedure of JIS Z 0237, a 25 mm width of eachpressure-sensitive adhesive tape was applied to an SUS 304 panel, leftto stand at 23° C. for 20 minutes and removed from the panel at an angleof 180 degrees at a pulling rate of 300 mm/min to measure a peel rate.

(Measurement of Adhesion to Polypropylene)

In accordance with the procedure of JIS Z 0237, a 25 mm width of eachpressure-sensitive adhesive tape was applied to a polypropylene sheet,left to stand at 23° C. for 20 minutes and removed from the sheet at anangle of 180° at a pulling rate of 300 mm/min to measure a peel rate.

(Measurement of Adhesion to Oil Surface)

A stainless steel (SUS) panel was precoated with 6 g/m² of rustpreventing oil and left to stand for one day to prepare an adherend. Inaccordance with the procedure of JIS Z 0237, a 25 mm width of eachpressure-sensitive adhesive tape was applied to the adherend, left tostand at 23° C. for 20 minutes and stripped from the sheet at an angleof 180° at a pulling rate of 300 mm/min to measure a peel rate.

Measurement results for SP adhesion, adhesion to polypropylene (PPAdhesion) and adhesion to oil surface are shown in Table 1. As can beappreciated from Table 1, the acrylic pressure-sensitive adhesives showgood adhesion to all of a metal surface, a polyolefin surface and an oilsurface.

TABLE 1 Adhesion to SP Adhesion PP Adhesion Oil Surface (kg/25 mm)(kg/25 mm) (kg/25 mm) Example 1 1200 1000 700 Example 2 1750 1370 830Comparative  570  280  10 Example 1

EXAMPLE 3

450 g of butyl acrylate ester (BA), 60 g of “KRATON LIQUID PolymerL-1253” (product of Shell Chemical) as the olefinic copolymer (b)terminally modified with a free-radically polymerizable unsaturateddouble bond, 90 g of AA-6, designated in the trade and manufactured byToagosei Co., Ltd., as the polymer (c) terminally modified with afree-radically polymerizable unsaturated double bond and having a numberaverage molecular weight of 2,000-30,000 and a glass transitiontemperature of at least 30° C., 450.91 g of toluene as a solvent wereblended in a 2 L separable flask equipped with a stirrer, coolingcondenser, thermometer and nitrogen inlet. The resulting liquid-formmonomer mixture was bubbled with nitrogen for 20 minutes to removetherefrom dissolved oxygen. An interior of the separable flask wassubsequently substituted with a nitrogen gas. Then, the monomer mixturewas elevated in temperature using a water bath while stirred at 100 rpm.

At the point when a reflux liquid appeared in the cooling condenser,0.30 g of 1,1-di(t-hexylperoxy)-3,3,5-tri methyl cyclohexane (productname: PERHEXA TMH, manufactured by NOF Corp.) was dissolved in about 1 gof ethyl acetate and then added, as a polymerization initiator, to themonomer mixture to initiate boiling-point polymerization.

After the passage of one hour, 0.60 g of PERHEXA TMH was dissolved inabout 1 g of ethyl acetate and again added to the mixture. After thepassage of 2, 3 and 4 hours from the start of polymerization, 0.6 g,1.20 g and 1.80 g of di(3,5,5-trimethylhexanoyl)peroxide (product name:PEROYL 335, manufactured by NOF Corp.), respectively dissolved in about1 g of ethyl acetate, were added. The boiling-point polymerization wascontinued for 8 hours to obtain an acrylic copolymer.

EXAMPLE 4

The procedure of Example 1 was followed, except that the monomer mixturewas used incorporating 450 g of butyl acrylate ester, 60 g of KRATONLIQUID Polymer L-1253, designated in the trade and manufactured by ShellChemical, as the olefinic copolymer (b) terminally modified with afree-radically polymerizable unsaturated double bond and 1.3 g ofglycidyl methacrylate as the polymerizable monomer (d), to obtain anacrylic copolymer (X-1).

Apart from the above, 450 g of methyl methacrylate (MMA), 4.14 g ofmercaptoacetic acid and 0.45 g of azobisisobutyronitrile were blended ina 2 L separable flask equipped with a stirrer, cooling condenser,thermometer and nitrogen inlet. The following boiling-pointpolymerization resulted in obtaining a polymer (e) having a weightaverage molecular weight of about 10,000 and a glass transitiontemperature Tg=about 90° C.

Then, the above-obtained acrylic copolymer (X-1) and polymer (e) weremixed together and heated with stirring to allow them to react for 8hours. As a result, an objective acrylic copolymer was obtained.

EXAMPLE 5

The procedure of Example 1 was followed, except that the monomer mixturewas used incorporating 492 g of butyl acrylate ester, 18 g of acrylicacid as the polymerizable monomer (d), 90 g of AA-6, designated in thetrade and manufactured by Toagosei Co., Ltd., as the polymer (c)terminally modified with a free-radically polymerizable unsaturateddouble bond and having a number average molecular weight of 2,000-30,000and a glass transition temperature of at least 30° C. and 450.91 g oftoluene as a solvent, to obtain an acrylic copolymer (X-3).

33 g of a 50 wt. % solution of an olefinic polymer (f) having an epoxygroup at its one end (product name: KRATON LIQUID Polymer EKP-207,manufactured by Shell Chemical) in toluene was added to 100 g of theabove-obtained acrylic copolymer solution. The subsequent mixing withstirring resulted in obtaining an objective acrylic copolymer.

EXAMPLE 6 Step 1

540 g of butyl acrylate ester (BA), 60 g of olefinic copolymer (b)terminally modified with a free-radically polymerizable unsaturateddouble bond (product name: KRATON LIQUID Polymer L-1253, manufactured byShell Chemical Co.), 0.36 g of t-butyl peroxyallyl carbonate (productname: PEROMER AC, manufactured by NOF Corp.) as the compound (I)containing both a free-radically polymerizable unsaturated double bondand a peroxide bond in a molecule, 0.27 g of dodecylmercaptan (DDM) as achain transfer agent, 0.30 g of benzyl methyl ketal (product name:IRGACURE, manufactured by Ciba Geigy Co.) as a photoinitiator and 490.91g of toluene as a polymerization solvent were blended in a 2 L separableflask equipped with stirrer, cooling condenser, thermometer and nitrogeninlet.

The resulting liquid-form monomer mixture was bubbled with nitrogen for20 minutes to remove therefrom dissolved oxygen. Then, the monomermixture was further bubbled with nitrogen and stirred at a velocity of100 rpm, during which time it was exposed to a 365 nm light at anintensity of 2 mW using a chemical lump to initiate polymerization. Thestart of polymerization was recorded at the point when the temperatureelevation was observed. The polymerization reaction was continued for 4hours.

Step 2

The polymer-toluene solution obtained in step 1, weighing 409 g, wascharged into a 2 L separable flask equipped with stirrer, coolingcondenser, thermometer and nitrogen inlet. 55.05 g of MMA monomer wasadded such that the polymer obtained in step 1 and methyl methacrylate(MMA) were blended in the solids ratio (weight ratio) of 80 to 20.

Also, 36.42 g of toluene as a polymerization solvent was added such thata total solids content amounted to 55% by weight.

The above-prepared liquid-form monomer mixture was bubbled with nitrogenfor 20 minutes to remove therefrom dissolved oxygen. An interior of theseparable flask was subsequently substituted with a nitrogen gas. Then,the monomer mixture was elevated in temperature using a water bath whilestirred at 100 rpm. The start of polymerization was recorded at thepoint when a reflux liquid appeared in the cooling condenser. Theboiling-point polymerization was continued for 4 hours. As a result, anobjective acrylic copolymer was obtained.

COMPARATIVE EXAMPLE 2

510 g of butyl acrylate ester (BA) and 90 g of the polymer (c)terminally modified with a free-radically polymerizable unsaturateddouble bond and having a number average molecular weight of 2,000-30,000and a glass transition temperature of at least 30° C. (product name:AA-6, manufactured by Toagosei Co., Ltd.) were used. The olefiniccopolymer (b) terminally modified with a free-radically polymerizableunsaturated double bond (product name: KRATON LIQUID Polymer L-1253,manufactured by Shell Chemical) was excluded. Otherwise, the procedureof Example 3 was followed to obtain an acrylic copolymer.

COMPARATIVE EXAMPLE 3

510 g of butyl acrylate ester (BA) was used. The olefinic copolymer (b)terminally modified with a free-radically polymerizable unsaturateddouble bond (product name: KRATON LIQUID Polymer L-1253, manufactured byShell Chemical) and the polymer (c) terminally modified with afree-radically polymerizable unsaturated double bond and having a numberaverage molecular weight of 2,000-30,000 and a glass transitiontemperature of at least 30° C. (product name: AA-6, manufactured byToagosei Co., Ltd.), were excluded. Otherwise, the procedure of Example3 was followed to obtain an acrylic copolymer.

COMPARATIVE EXAMPLE 4

The procedure of Example 4 was followed, except that the olefiniccopolymer (b) terminally modified with a free-radically polymerizableunsaturated double bond (product name: KRATON LIQUID Polymer L-1253,manufactured by Shell Chemical) was excluded, to obtain an acryliccopolymer.

COMPARATIVE EXAMPLE 5

The procedure of Example 4 was followed, except that glycidylmethacrylate as the polymerizable monomer (d) having a functional groupwas excluded and that the polymer (e) was not used, to obtain an acryliccopolymer.

COMPARATIVE EXAMPLE 6

Butyl acrylate ester (BA) was used in the amount of 510 g. The polymer(c) terminally modified with a free-radically polymerizable unsaturateddouble bond and having a number average molecular weight of 2,000-30,000and a glass transition temperature of at least 30° C. (product name:AA-6, manufactured by Toagosei Co., Ltd.) was used in the amount of 90g. The olefinic polymer having an epoxy group at its one end (productname: KRATON LIQUID Polymer EKP-207, manufactured by Shell Chemical) wasexcluded. Otherwise, the procedure of Example 5 was followed to obtainan acrylic copolymer.

COMPARATIVE EXAMPLE 7

Butyl acrylate ester (BA) and acrylic acid were used in amounts of 582 gand 18 g, respectively. The polymer (c) terminally modified with afree-radically polymerizable unsaturated double bond and having a numberaverage molecular weight of 2,000-30,000 and a glass transitiontemperature of at least 30° C. was excluded. Otherwise, the procedure ofExample 5 was followed to obtain an acrylic copolymer.

COMPARATIVE EXAMPLE 8

Butyl acrylate ester (BA) was used in the amount of 600 g. The olefiniccopolymer terminally modified with a free-radically polymerizableunsaturated double bond (product name: KRATON LIQUID Polymer L-1253,manufactured by Shell Chemical) was excluded. Otherwise, the procedureof Example 6 was followed to obtain an acrylic copolymer.

COMPARATIVE EXAMPLE 9

Butyl acrylate ester (BA) was used in the amount of 600 g. The olefiniccopolymer terminally modified with a free-radically polymerizableunsaturated double bond (product name: KRATON LIQUID Polymer L-1253,manufactured by Shell Chemical) was excluded. In step 2, a butylacrylate ester (BA) was used in the place of methyl methacrylate (MMA)Otherwise, the procedure of Example 6 was followed to obtain an acryliccopolymer.

Evaluation of Examples and Comparative Examples

Each of the acrylic copolymers obtained in Examples and ComparativeExamples was coated on a surface of a 38 μm thick polyester film(product number #381, manufactured by Lintec Corporation) to a thicknessof 15 μm and then dried at 110° C. for 5 minutes to thereby obtainpressure-sensitive tapes.

The following procedures were utilized to measure (1) SP adhesion, (2)adhesion to polyethylene and (3) holding power at 40° C. for theabove-fabricated pressure-sensitive tapes.

(1) SP adhesion: According to JIS Z 0237, a 25 mm width of eachpressure-sensitive adhesive tape was applied to a stainless steel panel(SUS 304 panel), left to stand at 23° C. for 20 minutes and removed fromthe panel at an angle of 180° at a pulling rate of 300 mm/min to measurea peel strength which was recorded as the SP adhesion.

(2) Adhesion to polyethylene: A 25 mm width of each pressure-sensitiveadhesive tape was applied to a polyethylene resin panel (product name:HIZEX 1300J, manufactured by Mitsui Petro. Chem. Ind. Co., Ltd.) as alow-polarity adherend, left to stand at 23° C. for 20 minutes andremoved from the panel at an angle of 180° at a pulling rate of 300mm/min to measure a peel strength which was recorded as the adhesion topolyethylene.

(3) Holding Power at 40° C.: According to JIS Z 0237, a 25 mm×25 mmplanar dimension of each pressure-sensitive adhesive tape was applied toa stainless steel panel (SUS 304 panel), left to stand at 23° C. for 20minutes and aged in a thermostatic chamber controlled at 40° C. for onehour. Thereafter, a suspension load of 1 g was applied to measure adistance that the pressure-sensitive adhesive tape after one hourdisplaced or a time from application of the load till dropage of theload, which was recorded as the holding power at 40° C.

The results for (1) SP adhesion, (2) adhesion to polyethylene and (3)holding power at 40° are given in the following Table 2.

TABLE 2 Cohesion (mm/min.) Peel Strength (g/25 mm) Holding Power SPAdhesion Adhesion to PE at 40° C. Ex.3 750 530 0.1 mm Displaced Ex.4 800620 0.1 mm Displaced Ex.5 780 560 0.15 mm Displaced Ex.6 680 500 0.05 mmDisplaced Comp.Ex.2 830 100(*1) 0.2 mm Displaced Comp.Ex.3 180(*1)30(*1) Dropped After 10 min. Comp.Ex.4 830 30(*1) 0.1 mm DisplacedComp.Ex.5 180(*1) 420 Dropped After 10 min. Comp.Ex.6 830 100(*1) 0.2 mmDisplaced Comp.Ex.7 180(*1) 30(*1) Dropped After 10 min. Comp.Ex.8 830100(*1) 0.2 mm Displaced Comp.Ex.9 180(*1) 30(*1) Dropped After 10 min.*1: Slippery Interfacial Peeling

EXAMPLE 7

An acrylic copolymer/toluene solution was obtained in the same manner asin Example 3. Toluene was removed from the solution by a conventionalmethod to extract the acrylic copolymer.

High-density polyethylene (product designation: L4470, manufactured byAsahi Kasei Corp.) was formed into a 50 μm thick film. Theabove-obtained acrylic copolymer was coated on the high-densitypolyethylene film to a thickness of 10 μm. Further, they were thermallybonded to each other by hot pressing at 150° C. As a result, apressure-sensitive adhesive film sheet was obtained incorporating apressure-sensitive adhesive layer comprising the acrylicpressure-sensitive adhesive composition provided on a substratecomprising the high-density polyethylene film.

COMPARATIVE EXAMPLE 10

An acrylic copolymer/toluene solution was obtained in the same manner asin Comparative Example 3. Toluene was removed therefrom by aconventional method to extract the acrylic copolymer. Otherwise, theprocedure of Example 7 was followed to obtain a pressure-sensitiveadhesive film sheet incorporating a pressure-sensitive adhesive layercomprising the acrylic pressure-sensitive adhesive composition providedon a substrate comprising the high-density polyethylene film.

(Evaluation of Example 7 and Comparative Example 10)

The following procedures were utilized to evaluate initial adhesion,aged adhesion and weather resistance of the pressure-sensitive adhesivefilm sheets obtained in Example 7 and Comparative Example 10.

Measurement of Initial Adhesion

According to JIS Z 0237, a 25 mm width of each pressure sensitiveadhesive film sheet was applied to an SUS 304 panel, left to stand at23° C. for 20 minutes and removed from the panel at an angle of 180° ata pulling rate of 300 mm/min to measure a peel strength which wasrecorded as the initial adhesion.

Measurement of Aged Adhesion

According to JIS Z 0237, a 25 mm width of each pressure sensitiveadhesive film sheets was applied to an SUS 304 panel, left to stand at23° C. for 20 minutes, aged in a thermostatic chamber controlled at 23°C. or 40° C. for one week and removed from the panel at an angle of 180°at a pulling rate of 300 mm/min to measure a peel strength which wasrecorded as the aged adhesion.

Evaluation of Resistance to Weather and Light

According to JIS B 7753, each pressure sensitive adhesive film sheet wasexposed to a light from a sunshine weather meter (WEL-SUN-HC,manufactured by Suga Test Instruments Co., Ltd.) for a period of 500hours and removed from the panel at an angle of 180° at a pulling rateof 300 mm/min to measure a peel strength. This peel strength was used asan indication in evaluating the wether resistance and light resistance.

The results are given in the following Table 3.

TABLE 3 Ex. 7 Comp. Ex. 10 Initial Adhesion 150 gf 180 gf Aged 23° C.240 gf Adhesive Residue Adhesion 80° C. 300 gf Adhesive Residue WeatherResistance 320 gf Adhesive Residue Evaluation

EXAMPLE 8

An acrylic copolymer/toluene solution was obtained in the same manner asin Example 3. Toluene was removed from the solution by a conventionalmethod to extract the acrylic copolymer.

The hot-melt adhesive comprising this acrylic copolymer was measured forthe physical properties as itemized below.

Cohesion

The hot-melt adhesive was cut into a 5×5×5 mm size to prepare a teststrip. The test strip was applied to a vertically-held aluminum plateand placed in an 80° C. oven for 12 hours. Then, a sagging distance ofthe test strip was measured and recorded as the cohesion.

Melt Viscosity at 190° C.

A melt viscosity at 190° C. of the test strip was measured by aBrookfield viscometer (product of Tokimec Inc., velocity: 2.5 rpm,rotor: #HH4).

Adhesion

The hot-melt adhesive maintained at 190° C. was applied to a cleansurface of a polyethylene panel (1.5 mm thick and 20 mm wide) to athickness of 1 mm and a planar dimension of 10×20 mm. Then, its adhesivestrength under shear was measured and recorded as the adhesion.

Oxidation Resistance

The hot-melt adhesive was cut into a 10×10 mm square and 2 mm thick teststrip. The test strip was applied to a glass plate, placed in a 200° C.oven for 8 hours and then its color change was observed as an indicationof oxidation resistance.

COMPARATIVE EXAMPLE 11

An acrylic copolymer/toluene solution was obtained in the same manner asin Comparative Example 3. Toluene was removed therefrom by aconventional method to extract the acrylic copolymer. This acryliccopolymer, in the form of a hot-melt adhesive, was measured for thephysical properties in the same manner as in Example 8.

The results are given in the following Table 4.

TABLE 4 Oxidation Melt Viscosity Resistance Cohesion at 190° C. Adhesion(Visual (mm) (xE4) (kg/cm²) Inspection) Ex.8 0 5.5 6.2 Good Comp.Ex.11 07.0 3.5 Poor

EFFECTS OF THE INVENTIONS

As stated above, the acrylic copolymers in accordance with the firstthrough fifth inventions of the present application are of the structurein which various polymeric portions are grafted to the polymer backbonecomprised mainly of the above-specified alkyl (meth)acrylate ester (a).This permits provision of acrylic copolymers having various propertiesby designing various combinations of the polymeric backbone portion andpolymeric branch portions.

For example, combinations can be designed comprising the polymericbranch portions rendered low in polarity and the highly polar polymericbackbone portion comprised mainly of the alkyl (meth)acrylate ester (a).If derived from such combinations, acrylic pressure-sensitive adhesivesexhibit good adhesion to adherends having varied polarities. Also, whendesigned to comprise polymeric portions of different polarities, acryliccopolymers can be suitably used as agents for dispersing polybutadienerubber in an acrylonitrile-styrene copolymer resin or as impactmodifying resins.

Also, selecting combinations of the polymeric backbone and branchportions properly, in terms of glass transition temperature, results ineasy provision of acrylic copolymers suitable for use as variousmaterials. For example, the formation of a continuous phase by thepolymeric portions derived from polymers of high glass transitiontemperatures results in the provision of acrylic copolymers suitable foruse as compounds requiring high resistance to heat and impact or astoner resins. On the other hand, the formation of a continuous phase bythe polymeric portions derived from polymers of low glass transitiontemperatures results in the provision of acrylic copolymers suitable foruse as films requiring high strength and elongation, hot-meltpressure-sensitive adhesives, thermoplastic elastomers or the like.

The acrylic pressure-sensitive adhesive compositions in accordance withthe present invention are comprised chiefly of any of the acryliccopolymers in accordance with the first through fifth inventions.Accordingly, selecting combinations of the polymeric portions properlyresults in the provision of adhesive compositions which exhibit highadhesive properties to adherends varied in polarity over a wide range,including high- and low-polarity adherends, or which when cured exhibitheat resistance and low-temperature tackiness well-balanced at highlevels.

The acrylic pressure-sensitive adhesive tape or sheet provided in theother aspect of the present invention is fabricated by integrating, viacoextrusion, the polyolefinic substrate and pressure-sensitive adhesivelayer comprised of the pressure-sensitive adhesive composition inaccordance with the present invention. Accordingly, it can exhibit goodadhesive properties and removability and non-staining propertieswell-balanced at proper levels, which rely on the pressure-sensitiveadhesive composition in accordance with the present invention.

The acrylic hot-melt adhesives provided in the further aspect of thepresent invention are comprised chiefly of any of the acrylic copolymersin accordance with the first through fifth inventions. Accordingly, theyexhibit good adhesive properties over a wide temperature range andfurther, when cured, exhibit good weather resistance and highly-balancedmelt viscosity and cohesion. Hence, hot-melt adhesives can be providedwhich exhibit good adhesive properties and weather resistance and whichare applicable for various uses.

What is claimed is:
 1. An acrylic copolymer characterized as beingprepared via copolymerization of (a) an alkyl (meth)acrylate estercontaining 1-14 carbon atoms in the alkyl, (b) an olefinic polymer orcopolymer terminally modified by a free-radically polymerizableunsaturated double bond and (c) a polymer terminally modified by afree-radically polymerizable unsaturated double bond and having a numberaverage molecular weight of 2,000-30,000 and a glass transitiontemperature of at least 30° C.
 2. An acrylic copolymer characterized asbeing prepared by grafting a polymer (e) to an acrylic copolymer madevia copolymerization of (a) an alkyl (meth)acrylate ester containing1-14 carbon atoms in the alkyl, (d) a polymerizable monomer containingone type of functional group selected from carboxyl, hydroxyl, epoxy andisocyanate and (b) an olefinic polymer or copolymer terminally modifiedby a free-radically polymerizable unsaturated double bond, said polymer(e) having at its one end a functional group reactive with thefunctional group in the polymerizable monomer (d) and also having anumber average molecular weight of 2,000-30,000 and a glass transitiontemperature of at least 30° C.
 3. An acrylic copolymer being prepared bygrafting an olefinic polymer or copolymer (f) to an acrylic copolymer(X-2) made via copolymerization of (a) an alkyl (meth)acrylate estercontaining 1-14 carbon atoms in the alkyl and (d) a polymerizablemonomer containing one type of functional group selected from carboxyl,hydroxyl and isocyanate, said olefinic polymer or copolymer (f) havingat its one end one type of functional group reactive with the functionalgroup in the polymerizable monomer (d).
 4. An acrylic copolymercharacterized as being prepared by grafting an olefinic polymer orcopolymer (f) to an acrylic copolymer (X-3) made via copolymerization of(a) an alkyl (meth)acrylate ester containing 1-14 carbon atoms in thealkyl, (d) a polymerizable monomer containing one type of functionalgroup selected from carboxyl, hydroxyl, epoxy and isocyanate and (c) apolymer terminally modified by a free-radically polymerizableunsaturated double bond and having a number average molecular weight of2,000-30,000 and a glass transition temperature of at least 30° C., saidolefinic polymer or copolymer (f) having at its one end one type offunctional group reactive with the functional group in the polymerizablemonomer (d).
 5. acrylic copolymer characterized as being prepared by: afirst step wherein a compound (I) containing a free-radicallypolymerizable unsaturated double bond and a peroxide bond in a molecule,an alkyl (meth)acrylate ester (a) containing 1-14 carbon atoms in thealkyl and an olefinic polymer or copolymer (b) terminally modified by afree-radically polymerizable unsaturated double bond are allowed toundergo free-radical polymerization, with the aid of a photoinitiator,in the temperature range where the compound (I) is not caused todecompose; and a second step wherein a polymerizable monomer component(II) which differs in composition from the polymerizable monomercomponents used in the preceding free-radical polymerization is allowedto undergo free-radical polymerization, under the presence of theproduct of the preceding free-radical polymerization, in the temperaturerange where the compound (I) is caused to decompose.
 6. The acryliccopolymer as recited in claim 1, wherein said olefinic polymer orcopolymer (b) is an ethylene-butylene random copolymer or a propylenepolymer terminally modified by a free-radically polymerizableunsaturated double bond.
 7. The acrylic copolymer as recited in claim 2,characterized in that said olefinic polymer or copolymer (b) is anethylene-butylene random copolymer or a propylene polymer terminallymodified by a free-radically polymerizable unsaturated double bond, andthat the functional group of said polymerizable monomer (d) is an epoxygroup and the functional group of said polymer (e) is a carboxyl group.8. The acrylic copolymer as recited in claim 3, characterized in thatthe functional group of said polymerizable monomer (d) is a carboxylgroup.
 9. The acrylic copolymer as recited in claim 3, wherein thefunctional group of said polymerizable monomer (d) is a carboxyl groupand the functional group of said olefinic polymer (f) is an epoxy group.10. The acrylic copolymer as recited in claim 5, wherein polymerizablemonomer component (II) used in the second step has a glass transitiontemperature of at least 20° C.
 11. An acrylic pressure-sensitiveadhesive composition being comprised principally of the acryliccopolymer of claim
 1. 12. The acrylic pressure-sensitive adhesivecomposition as recited in claim 11, characterized as further including ahydrogenated petroleum resin.
 13. An acrylic pressure-sensitive adhesivetape or sheet being prepared by integrating, by extrusion, apolyolefinic substrate and a pressure-sensitive adhesive layercomprising the pressure-sensitive adhesive composition of claim
 11. 14.An acrylic hot-melt adhesive comprised principally of the acryliccopolymer of claim 1.